Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $58.77   8.517%   $63.7754   $63.78   $63.80   $63.80  
  Purchase #2 $102.41   3.305%   $105.7947   $105.79   $105.80   $105.80  
  Purchase #3 $93.44   3.511%   $96.7207   $96.72   $96.70   $96.70  
  Purchase #4 $83.29   9.409%   $91.1268   $91.13   $91.15   $91.10  
  Purchase #5 $136.74   7.277%   $146.6906   $146.69   $146.70   $146.70  
  Purchase #6 $75.64   12.406%   $85.0239   $85.02   $85.00   $85.00  
  Purchase #7 $231.40   5.858%   $244.9554   $244.96   $244.95   $245.00  
  7 purchase totals = $781.69       $834.0875   $834.09   $834.10   $834.10